Page 726 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Respir atory system: 3.4 Medical conditions of the lower respir atory tr act 701

VetBooks.ir Clinical presentation activity, hyperaemia, oedema and bronchoconstric-
Bronchoscopy is useful to assess airway hyperre-
This condition is differentiated from horses with
IAD by the presence of respiratory difficulty at rest.
airway secretions (Fig. 3.161). BAL is the test of
A seasonal pattern of heaves exacerbation is often tion, and to evaluate the presence and nature of any
reported. Clinical signs during exacerbation fre- choice to diagnose heaves. BAL may be performed
quently include expiratory dyspnoea accompanied transendoscopically using the biopsy channel of a
by a visible ‘heave line’ as the external abdominal sterilised bronchoscope for fluid infusion and aspi-
oblique muscles are used to facilitate expiration. ration, or blindly using a flexible cuffed nasotra-
Nasal discharge is serous to mucopurulent, and inter- cheal catheter passed into the bronchi. Cytological
mittent to paroxysmal coughing may be observed. assessment of BAL fluid is required to determine
Flaring of the nostrils may be seen. Severe cases may the type(s) of leucocyte contributing to the airway
have depression, lack of interest in feed due to diffi- inflammation (Fig. 3.162). In general, an elevation
culty breathing, rocking of the animal as it breathes in the percentage of neutrophils (>25%) in the differ-
and a wheeze or tracheal rattles may be audible at the ential cell count is seen in animals during episodes
nares during expiration. of clinical exacerbation of heaves, although elevated
percentages of mast cells and eosinophils may also
Differential diagnoses be observed.
Pulmonary infections (viral or bacterial), intersti- Administration of N-butylscopolammonium bro-
tial pneumonia and pulmonary neoplasia may have mide (0.3 mg/kg i/v once), which has short-acting
a similar presentation. Animals with heaves are typi- bronchodilatory effects, may assist in the diagnosis
cally afebrile and have normal fibrinogen, in con- of heaves, as horses with pneumonia do not typically
trast to animals with infectious causes of respiratory respond to bronchodilators.
disease.

Diagnosis
Clinical history may suggest a seasonal pattern of 3.160
occurrence, corresponding with increased indoor
housing during periods of inclement weather such
as in the winter months. Lack of improvement in
response to antibiotic treatment is also frequently
reported.
Thoracic auscultation during use of a re-
breathing bag is indicated in all cases, except ani-
mals demonstrating signs of dyspnoea or respiratory
distress (Fig. 3.160). Frequently, crackles and
wheezes are identified over the lower airways and
movement of secretions within the trachea may be
audible. Percussion may reveal an expanded cau-
dodorsal margin to the lung field due to hyperinfla-
tion of the lungs as a consequence of air-trapping,
although this must be differentiated from a gas cap
in the caecum when percussing the right side of the
abdomen. Radiographic changes are not specific for
heaves and may include an increased interstitial and/
or bronchial pattern. Thoracic radiographs may be Fig. 3.160 Placement of a re-breathing bag.
helpful to exclude bronchopneumonia as a differen- The handler is taking care to prevent the bag from
tial diagnosis. obstructing the nostrils of the horse.